New improved antibiotics continue to be needed in veterinary medicine. For example, coccidiosis continues to be a wide-spread problem in the poultry industry. Coccidiosis results from infection by one or more species of Eimeria or Isospora (for a summary see Lund and Farr in "Diseases of Poultry," 5th ed, Biester and Schwarte, Eds., Iowa State University Press, Ames, Iowa, 1965, pp. 1056-1096). Economic losses due to coccidiosis are great, creating a demand for better anticoccidial agents.
Promotion of growth in ruminants, such as cattle and sheep, is another economically desirable objective of veterinary science. Of particular interest is growth promotion achieved by increasing feed-utilization efficiency. The mechansim for utilization of the major nutritive portion (carbohydrates) of ruminant feeds is well known. Microorganisms in the rumen of the animal degrade carbohydrates to produce monosaccharides and then convert these monosaccharides to pyruvate compounds. Pyruvates are metabolized by microbiological processes to form acetates, butyrates or propionates, collectively known as volatile fatty acids (VFA). For a more detailed discussion, see Leng in "Physiology of Digestion and Metabolism in the Ruminant," Phillipson et al., Eds., Oriel Press, Newcastle-upon-Tyne, England, 1970, pp. 408-410.
The relative efficiency of VFA utilization is discussed by McCullough in Feedstuffs, June 19, 1971, page 19; Eskeland et al. in J. An. Sci. 33, 282 (1971); and Church et al. in "Digestive Physiology and Nutrition of Ruminants," Vol. 2, 1971 pp. 622 and 625. Although acetates and butyrates are utilized, propionates are utilized with greater efficiency. Furthermore, when too little propionate is available, animals may develop ketosis. A beneficial compound, therefore, stimulates animals to produce a higher proportion of propionates from carbohydrates, thereby increasing carbohydrate-utilization efficiency and also reducing the incidence of ketosis.